Study finds plug-in hybrids are rarely charged by owners

A new study from the Fraunhofer Institute, a German research organization, reveals that plug-in hybrid electric vehicles (PHEVs) often fail to deliver on their efficiency promises because owners rarely charge them. Real-world data drawn from onboard computers shows that grid power is responsible for less than a third of total energy use for the 1 million PHEVs in Germany. Consequently, these vehicles produce about 3.5 times more emissions than their official ratings suggest, as the vast majority of drivers plug in only occasionally or not at all.

The performance gap is stark across different automotive manufacturers. At best, Toyota drivers used electricity for 44% of their driving energy, suggesting they plugged in the most frequently. By contrast, Porsche drivers used electricity for just 0.8% of their driving, averaging only 7 kilowatt-hours of grid power over two years. These vehicles are often limited by anemic batteries capable of powering the vehicle for short distances, typically about 20 to 30 miles. Because most PHEVs are based on fossil fuel platforms, the vehicles are likely to remain compromised when driving on electrons, as their electric motors are often unable to deliver 100% of the vehicle’s power needs.

Despite these findings, automakers in the U.S. continue to push future PHEV models as an appealing alternative for American drivers. Ford is among the companies promoting these vehicles as a bridge to full electrification, aiming to boost fleet-wide efficiency without a wide rollout of battery-electric vehicles (EVs). “We’re looking to make CO2 reductions across our lineup, but we’re doing it in a very efficient way,” Ford CEO Jim Farley said during an earnings call. However, the data suggests that without consistent charging, these vehicles fail to habituate drivers to electric power or provide the intended environmental benefits.

As the industry considers alternatives, some manufacturers are looking at extended-range electric vehicles (EREVs), which run on battery power until depleted, at which point a fossil fuel engine recharges the battery. BMW previously manufactured an EREV, and Stellantis has announced plans for EREV pickup trucks. Meanwhile, some consumers in Europe and the U.S. are bypassing the hybrid compromise entirely in favor of full EVs, such as the Kia EV9, as charging networks expand.

Why it matters

The “bridge” strategy for electrification relies on consumer behavior that is not actually occurring in the real world. If drivers do not regularly charge plug-in hybrids, the vehicles function as heavy, inefficient gasoline cars, complicating the transition to full battery-electric vehicles.